A number of different systems and methods for quickly chilling food, beverages, and other goods are in commercial use today. Chilling devices include those with refrigerant coils which directly chill liquid water to a set temperature which is then circulated in a tank to chill product, ice builders which harvest ice to chill water which is then pumped into a separate chill tank; slush ice builders where the slush formed is pumped into a separate chill tank; antifreeze systems using chilling agents such as brines, glycols or eutectic salts in a direct chill system; and air chill systems where the product is either chilled or frozen by contact with high-volume cold air.
Chilling or cooling systems using antifreeze, eutectics, brines, glycol and other additives have inherent sanitation and corrosion problems. Use of such additives which may be toxic is inappropriate for direct contact with food products. Disposal of tank fluids containing such chemicals can also create environmental problems and additional expense for proper disposal.
Thermal energy storage (or cool storage) is a process by which heat is extracted from a thermal reservoir (e.g., a chilling agent, such as water, to form frozen chilling agent or a slurry of frozen and liquid chilling agent, such as ice or slush) at one time, and at a later time to use the thermal reservoir (e.g., the ice or slush) to extract heat from an environment. Ice-building and harvesting systems are used to provide chilled water for air conditioning of buildings. Ice is built on refrigerator coils and later harvested into a separate storage tank to chill water that is then available for cooling. A significant benefit of such systems is their use of off-period ice building to reduce power costs. Typically, ice harvesting is done in these systems by application of external mechanically or thermal energy decreasing the overall efficiency of the cooling process. Exemplary systems using thermal energy storage for building air conditioning are discussed in U.S. Pat. Nos. 4,656,836; 4,928,493; and 5,168,724.
External ice builders (e.g., not within the chill tank) with heat exchangers are in common use in food manufacture and commissary kitchens. Ice is built on refrigerator coils and harvested to chill water. External energy is most often added to harvest the ice. In many applications, water chilled in the external ice builder is pumped at high volume into a chill tank containing product to be chilled. The product may be contained in bags or similar individual container which may be tumbled or agitated mechanically to speed chilling. Tumblers are expensive to build and can be dangerous for those personnel who operate, clean, load and unload them. Chill times can be relatively long in such systems (up to several hours) at least in part because the temperature of the near-freezing water in the ice builder is typically several degrees higher in temperature after it is transferred to the chill tank for cooling the product. Furthermore, the capacity of chilled water to remove heat with concomitant temperature rise is only a small fraction of that of an equal volume of ice to remove heat with concomitant melting of the ice. Additionally, while refrigeration units are typically light enough to be placed on the roof of a building to conserve floor space, ice builders with a water/ice storage tanks are generally too heavy to put on a roof of a building and thus can require allocation of more floor space or ground space than a chill tank alone. Further, it is more efficient and less costly to run refrigerant supply and return lines than it is to run supply and return lines for high volumes of liquid chilling agent or slush. The distance that chilling agent or slush is transported is a limiting factor on system efficiency.
In slush ice chilling systems, slush ice is made in a separate tank and either scraped off mechanically or removed by running high-pressure water through polished large diameter tubes and then transported to a chill tank. Slush ice systems consume energy in harvesting and transferring the slush ice to chill the product. Solid ice is generally preferred to slush for storage of cooling thermal energy, because slush ice has a significantly lower latent heat of fusion than an equal volume of solid ice.
All of these systems for chilling goods introduce energy needlessly, waste space, or create other avoidable expenses. The present invention is directed to a quick chilling device that employs thermal energy storage to improve chilling efficiency and speed, but avoids additional energy input to harvest ice or slush.